1. Field of the Invention
The present invention relates to a sponge blasting apparatus which jets against a work a blasting medium of sponge fragments formed of abrasives stuck within a porous elastic body, and thereby roughens the surface of the work to prepare it for further machining, and a sponge blasting method.
2. Description of the Related Art
When a painted wall surface is to be repainted, blasting is carried out as a preparatory step to grind the coat of the wall surface, roughen the coated surface and thereby to make it ready to be repainted.
Such blasting has been traditionally accomplished by using sand as the blasting medium as described in Japanese Patent Application Laid-Open No. 9-109029 and elsewhere. Sand blasting is a process by which a sand-containing air jet blown out of a nozzle at high speed is caused to hit against the painted surface, and the painted coat of the surface is ground off with the impact of the blast to roughen the surface.
However, since the blasting medium bounce off with a strong force in a sand blasting process, it entails a problem of the scattering of fine dust. Moreover, the operator who manipulates the nozzle has to wear heavy clothes to protect oneself against the blasting medium bouncing off with a strong force, and accordingly cannot move flexibly. Furthermore, since the operator's field of view is blurred by the scattering dust, it is difficult for him to accomplish his task in uniform quality.
With a view to solving these problems, the so-called sponge blasting came to be known, which uses as the blasting medium sponge fragments formed of abrasives stuck within a porous elastic body.
By this sponge blasting, when the sponge blasting medium blown out of a nozzle with a high speed air jet is caused to hit against the painted surface, the blasting medium becomes flat and the contained abrasives directly hit the painted surface at high speed. In this way, the painted coat can be ground and removed as in sand blasting. There also is an advantage that fine dust, which would otherwise drift in the air, is sucked into the sponge fragments, and accordingly the dust scattering can be reduced. Sponge blasting has a further advantage that, as the repulsive force is also absorbed by the sponge fragments, the bouncing off of the blasting medium is dramatically reduced, and accordingly the operator who manipulates the nozzle need not wear so heavy protective clothing.